The thin body has long been considered ‘normal' in Western culture, whereas the anorexic body has been framed as pathological despite the fact that both bodies often engage in regimes of undereating and extreme exercising which dovetail with one another. Pro-anorexia (or ‘pro-ana') online spaces, which emerged in the late twentieth century, have been criticised for their espousal of anorexia even though much of the advice they provide and the images they collate, derive from mainstream culture. Censorship and vilification by the media have meant that since their inception these spaces have undergone a number of changes. This thesis therefore investigates the thin ideal in pro-ana online spaces at a time when the boundaries between the mainstream espousal of thinness and the body image promoted in pro-ana culture are becoming increasingly blurred. Drawing on empirical research across a range of websites, forums, and social media which identify as pro-ana, I employ textual analysis to explore how thinness is constructed in these spaces. My investigation produced a set of themes which shape this thesis. Central were: the denial and disguise of disordered-eating practices; the pre-eminence of the white, middle-class, heterofeminine body; and the importance of pain in realising the thin ideal. The central claim of this thesis is that pro-ana online spaces expose the extent to which normative femininity is underpinned by practices which may be deeply disordered, but they are viewed as normal by mainstream culture. Pro-ana culture illustrates an extreme response to achieving thinness but it also critiques the ideal to which it aspires. Hence, this thesis concludes by turning to the potential for resistance in pro-ana online spaces and arguing that although they do not uncritically conform to the culture of compulsory thinness, they are nonetheless postfeminist enclaves which perpetuate the primacy of the individual.